Valid Friday June 30, 2017 to Tuesday July 11, 2017
US Hazards Outlook
NWS Climate Prediction Center College Park MD
EDT June 27 2017Synopsis
: A couple of low pressure systems are
expected to progress east along a nearly stationary front extending across the
Great Lakes, Midwest, and central Great Plains during the next week. An area of
upper-level high pressure is forecast to build over the high Plains by the 4th
of July and then expand east during Week-2. Hurricane Dora in the east Pacific
is forecast to weaken as it tracks near the 20th parallel prior to this period.
An area of upper-level high pressure is expected to persist over eastern
mainland Alaska through the first week of July. Hazards
Detailed Summary For
Friday June 30 - Tuesday July 04:
- Heavy rain extending from New England and the Great Lakes southwest to
the southern Great Plains, Fri-Sat, Jun 30-Jul 1.
- Heavy rain for parts of the northern and central Great Plains along with
the Midwest, Sun-Mon, Jul 2-3.
- Heavy rain for parts of Kodiak Island, the Kenai peninsula, and the Prince
William Sound, Fri-Sat, Jun 30-Jul 1.
- Much above-normal temperatures for parts of the northern and central Great
Plains, Mon-Tue, Jul 3-4.
- Much above-normal temperatures for the upper Yukon Valley of Alaska,
Mon-Tue, Jul 3-4.
- Excessive heat for parts of the central U.S., Thu-Fri, Jul 6-7.
- Slight risk of much above-normal temperatures for parts of the central and
eastern U.S., Wed-Mon, Jul 5-10.
- Slight risk of much above-normal temperatures for parts of eastern mainland
Alaska, Wed-Sun, Jul 5-9.
- Flooding occurring, imminent, or likely for parts of Wyoming, the Midwest,
- Severe Drought across California, Hawaii, the Northern Plains, and the
Heavy rainfall and flash flooding remain
the primary concerns across the central U.S. this week, followed by an
increasing risk of a heat wave during early July. Model guidance remains
consistent that abundant low-level moisture will develop across much of the
eastern and central U.S. with the deterministic 6Z GFS model indicating
precipitable water values increasing to more than 1.75 inches, focused along a
front. Heavy rainfall (1 to 3 inches, locally more) is likely along this front,
extending from New England and the Great Lakes southwest to the southern Great
Plains on June 30 and July 1. The most likely area for heavy rain is then
expected to shift back to the north across the northern/central Great Plains
and Midwest on July 2 and 3. The depicted heavy rain hazards are based on the
precipitation forecasts from the 6Z GFS and 0Z ECMWF ensemble means. Given the
high moisture content of the atmosphere, thunderstorms throughout the central
and eastern U.S. will be capable of triggering flash flooding this week. Severe
weather, primarily damaging wind and large hail, could also occur in the
strongest thunderstorms, but low predictability precludes a designation of a
specific severe weather hazard at this time.
An upper-level ridge is expected to strengthen over the high Plains by
early next week and begin to expand east across the central U.S. Therefore,
much above-normal temperatures (10 degrees F or more) are forecast to affect
the northern and central Plains on July 3 and 4. Maximum temperatures are
expected to warm well into the 90s to near 100 degrees F by July 4 across this
region. This heat is likely to worsen ongoing drought conditions across eastern
Montana and the Dakotas.
On June 30 and July 1, a low pressure system with onshore flow is expected
to bring heavy rainfall (locally more than 1.5 inch per 24 hours) across Kodiak
Island, the southeast Kenai peninsula, and the Prince William Sound. Strong
ridging aloft is expected to result in much above-normal temperatures across
the Yukon River Valley where maximum temperatures above 85 degrees F are
forecast on July 3 and 4. For Wednesday July 05 - Tuesday
The 6Z GFS and 0Z ECMWF ensemble means agree with an amplified
ridge centered over the Great Plains during Week-2. This anomalous ridging
supports a slight risk of much above-normal temperatures for parts of the
central and eastern U.S. through at least July 10. The outlined slight risk
area is generally consistent with the GEFS reforecast tool which features a
broad area where maximum temperatures have a 20 to 30 percent chance of
exceeding the 85th percentile compared to climatology. Although only a slight
risk for much above-normal temperatures is posted, heat index values may exceed
105 degrees F in the more humid areas of the central and eastern U.S. Based on
850-hpa temperatures predicted by the deterministic GFS model, the GEFS
calibrated heat index forecast, and climatology, an excessive heat hazard is
posted for parts of the central U.S. on July 6 and 7.
A slight risk of much above-normal temperatures is also posted for parts of
eastern mainland Alaska through July 9 due to persistent ridging aloft. The
deterministic GFS model remains consistent with maximum temperatures warming to
near 90 degrees F across the upper Yukon Valley early in Week-2.
An upper-level ridge is forecast to shift slightly north to the Four
Corners region which would lead to increased moisture across the desert
Southwest. This increasing moisture is expected to result in more convection
and a higher risk of flash flooding across Arizona and New Mexico during Week-2.
The U.S. Drought Monitor valid on June 20 shows D2-D4 drought coverage over
the CONUS now at 2.13%, a slight increase from 1.57% one week ago. This
increase is tied to the emergence of severe drought in the Northern
Forecaster: Brad Pugh
Click here to see a display of the GFS Ensemble Forecasts
Please consult local NWS Forecast Offices for short range forecasts and region-specific information.